EP0529672B1 - Elément d'affichage à cristal liquide et appareil d'affichage à cristal liquide utilisant celui-ci - Google Patents

Elément d'affichage à cristal liquide et appareil d'affichage à cristal liquide utilisant celui-ci Download PDF

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Publication number
EP0529672B1
EP0529672B1 EP92114825A EP92114825A EP0529672B1 EP 0529672 B1 EP0529672 B1 EP 0529672B1 EP 92114825 A EP92114825 A EP 92114825A EP 92114825 A EP92114825 A EP 92114825A EP 0529672 B1 EP0529672 B1 EP 0529672B1
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EP
European Patent Office
Prior art keywords
liquid crystal
crystal display
display element
solidified matrix
light
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EP92114825A
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German (de)
English (en)
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EP0529672A3 (en
EP0529672A2 (fr
Inventor
Yoshiharu Ag. Technology Co. Ltd. Ooi
Yoshinori Ag. Technology Co. Ltd. Hirai
Satoshi Ag. Technology Co. Ltd. Niiyama
Tsuneo Ag. Technology Co. Ltd. Wakabayashi
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AG Technology Co Ltd
Amersham Biosciences Membrane Separations Corp
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AG Technology Co Ltd
AG Technology Corp
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Publication of EP0529672A3 publication Critical patent/EP0529672A3/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/133371—Cells with varying thickness of the liquid crystal layer
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/133397—Constructional arrangements; Manufacturing methods for suppressing after-image or image-sticking
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133553—Reflecting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/30—Gray scale

Definitions

  • the present invention relates to a liquid crystal display element including liquid crystal dispersed and held in a solidified matrix and a liquid crystal display apparatus using such display element.
  • liquid crystal displays have been widely used for personal word processors, hand-held computers, portable TV sets and so on, taking the advantages of low power consumption, low driving voltage and so on.
  • liquid crystal display elements having an active element for each picture element electrode have particularly been noted and developed.
  • liquid crystal display elements As such liquid crystal display elements, there was a proposal on liquid crystal display elements in which a dynamic scattering mode (DSM) liquid crystal is used.
  • DSM dynamic scattering mode
  • the liquid crystal display element of this type had a disadvantage of large current consumption because a high value of electric current passed in the DSM liquid crystal.
  • liquid crystal display elements in which a twist nematic (TN) type liquid crystal is used have been widely used. For instance, portable TVs have been widely commercialized. Since the TN type liquid crystal display element has a very small leak current and a small power consumption, it is suitable for using a battery as a power source.
  • a liquid crystal and solidified matrix composite in which a nematic liquid crystal is dispersed and held in a solidified matrix such as a polymer matrix is used, and a low voltage such as 10 V or lower is sufficient to drive it by utilizing the transparent-scattering characteristics.
  • the applied voltage-transmittance characteristic of the liquid crystal and solidified matrix composite generally shows a strong non-linearity in comparison with that of a conventional TN mode liquid crystal element, and accordingly, when a gray scale display is to be effected, it is necessary to carry out the modulation of an input signal voltage in response to the applied voltage-transmittance characteristic, namely, a ⁇ correction having a strong non-linearity.
  • the present invention provides a liquid crystal element as claimed in claim 1 and a projection type liquid crystal display apparatus as claimed in claim 7.
  • Advantageous features are as claimed in the dependent claims.
  • liquid crystal display element of the present invention polarization plates are not required because the liquid crystal and solidified matrix composite capable of controlling a scattering state and a transparent state is used. Accordingly, the transmittance of light in a transparent state can be substantially improved, and a bright display is possible. In particular, when the liquid crystal display element is used for a projection type display, a projection type display having brightness and good contrast ratio is obtainable.
  • the liquid crystal and solidified matrix composite used for the liquid crystal display element of the present invention can provide an effect of controlling image-sticking caused by hysteresis, which is the greatest advantage of the present invention, even in a mode other than a transparent-scattering type mode, as far as a liquid crystal display element comprising liquid crystal and a solidified material is used.
  • the liquid crystal and solidified matrix composite can be used for a transparent-absorption type liquid crystal display element or the like which comprises a guest-host type liquid crystal obtained by dissolving a dichroic dye in liquid crystal.
  • the present invention since at least one substrate with an electrode of the pair of substrates with electrodes has a fine concave-convex electrode surface at the side of the liquid crystal and solidified matrix composite, an image-sticking phenomenon due to hysteresis inherent in the liquid crystal and solidified matrix composite can be controlled, whereby a beautiful display can be obtained even in a half tone display.
  • the liquid crystal and solidified matrix composite is used as a reflection type liquid crystal display element, there is an advantage that the concave-convex electrode surface controls regular reflection to thereby improve a contrast ratio of display.
  • the liquid crystal display element of the present invention can be used not only as a direct view type display element but also as a projection type display element.
  • a display element may be constituted in combination with a backlight, a lens, a prism, a mirror, a diffusion plate, a light absorbing material, a color filter and so on in accordance with display characteristics which are desired to obtain.
  • the reduction of the hysteresis on the applied voltage-transmittance characteristics of the liquid crystal and solidified matrix composite can be attained by suitably using material for liquid crystal, material for forming a solidified material by curing a polymeric material, and by optimizing the structure of the liquid crystal and solidified matrix composite.
  • a severe controlling technique is required in order to obtain a high quality of display.
  • the hysteresis (or an optical problem caused by the hysteresis) can be apparently reduced to a practically negligible extent even when there is more or less the hysteresis. Accordingly, the present invention is advantageous in that a range of selecting materials used is widened and margins in manufacturing the liquid crystal display element are enlarged.
  • the threshold voltage on the applied voltage-transmittance characteristics is scattered. Namely, even when a liquid crystal and solidified matrix having a hysteresis characteristic is used, the threshold voltage is scattered because of a distribution of electric field across the liquid crystal and solidified matrix composite according to the distribution of the electrode gap, and there is obtainable an electro-optical characteristic as the mean value of the electrode gap of various portions. Accordingly, the apparent hysteresis is reduced.
  • Figure 1 is an enlarged cross-sectional view of an embodiment of the liquid crystal display element according to the present invention.
  • reference numeral 1 designates a liquid crystal display element
  • numeral 2 designates a substrate having a concave-convex surface which is made of a material such as glass, plastics or the like
  • numeral 3 designates an electrode such as ITO (In 2 O 3 -SnO 2 ), SnO 2 or the like
  • numeral 4 designates a substrate having a flat surface made of a material such as glass, plastics
  • numeral 5 designates an electrode such as ITO (In 2 O 3 -SnO 2 ), SnO 2 , Al, Cr or the like
  • numeral 6 designates a liquid crystal and solidified matrix composite such as a liquid crystal and polymer composite held between the both substrates (electrodes).
  • the substrate depicted at the left side of the drawing is the substrate having an electrode surface having concave and convex portions.
  • the formation of the concave-convex surface may be formed by blasting fine particles, grinding, etching or another suitable treatment on the substrate.
  • the electrode may be prepared.
  • An insulator layer or a smoothing layer or another layer may be formed additionally on the electrode layer having a concave-convex surface corresponding to the substrate surface.
  • the concave-convex portions may be formed by means of an electrode having concave-convex portions while the substrate is formed flat.
  • the thickness of a liquid crystal and polymer composite may be uniform by forming a smoothing layer on the concave-convex electrode surface.
  • the electrodes for the both substrates should be transparent.
  • either one of the electrodes should be a reflection electrode of metal or in combination of a transparent electrode and a reflection layer to obtain the reflection of light.
  • Each picture element may be provided with an active element such as a TFT (thin film transistor), a thin film diode, a MIM or the like.
  • a picture element electrode may be a transparent electrode while wiring on the substrate for the active element is of metal so as to be an opaque electrode. Further, a photo-sensitive layer is laminated to the substrate for use of writing by light.
  • the active element When the active element is to be arranged, it is normally disposed at a flat surface side of the substrate.
  • a light beam for the display element with a photoconductive layer or an electronic gun may be used to supply an electric charge in a picture element instead of the application of a voltage to a picture element by means of an active element.
  • the effective optical-path in a liquid crystal and solidified matrix composite of a reflection type display element is twice longer than that of a transmissive type display element. Then, in a scattering state, the scattering ability of a reflection type display element is more than that of a transmissive type display element. As a result, the performance of a display apparatus comprising a reflection type display element can be improved compared with a display apparatus comprising a transmissive type display element. (For example, lower driving voltage, higher contrast ratio or brighter image can be achieved.)
  • the regular reflection of light at the outer and inner surfaces of the substrate disposed at the front side may cause the reduction of the contrast ratio.
  • the regular reflection at the interface between the inner surface of the substrate and a liquid crystal and polymer composite can be reduced by using a substrate having a concave-convex electrode surface at the front side.
  • both advantages of the improvement of hysteresis and a glare control can be simultaneously obtained by using a substrate having a concave-convex electrode surface.
  • an aperture as a device for reducing diffusion light which is described hereinafter is used. Accordingly, since almost all the reflection light of scattered light at the interface of the substrate having a concave-convex electrode surface does not pass through the aperture because the reflection light becomes diffusion light, whereby the contrast ratio of a projection image is improved.
  • a concave-convex structure constituted by an inclined surface inclined at a suitable angle of inclination is more effective to remove the scattering at the interface of the substrate, than a concave-convex structure of a rectangular shape having a flat surface. It is preferable that the angle of inclination to the surface of reflection is in a range of from about 2° to 30°.
  • Using a reflection type display element improves the scattering ability of the display apparatus. Accordingly, the degree of collimation for incident light into the display element for same screen contrast ratio is relaxed. As a result, a brighter projection image can be realized compared with the display apparatus comprising a transmissive type display element.
  • both advantage of the improvement of hysteresis and the formation of a diffusion reflector can be simultaneously obtained by using a substrate having a concave-convex reflection electrode surface.
  • the pitch of the concave-convex portions in the substrate having a concave-convex electrode surface is smaller than the size of the picture element for display.
  • the size of the element is relatively small while the size of a picture element is usually in a range of from about 30 ⁇ m to 200 ⁇ m.
  • a pitch of concave-convex portions should be smaller than the size of the picture element.
  • the pitch is preferably 100 ⁇ m or lower for the projection type active matrix display element.
  • the effect of averaging the electro-optical characteristic decreases, and the reduction of the image-sticking due to the hysteresis can not be expected.
  • the smallest scale of the effect of averaging the electro-optical characteristic is determined by the size of liquid crystal droplets dispersed and held in a solidified matrix.
  • the transparent-scattering characteristics of the display element of the present invention is obtainable by causing a change of arrangement of liquid crystal molecules in liquid crystal droplets by the application of an electric field, whereby there is a change of the refractive index of the liquid crystal for the incident light used. Accordingly, it is necessary that the pitch of the concave-convex portions of the display element is equal to or greater than the diameter of liquid crystal droplets in order to reduce the image-sticking phenomenon.
  • the pitch P of the concave-convex portions is twice or more as the diameter of the liquid crystal droplets. Accordingly, it is preferable that the relation of the pitch P of the concave-convex portions to the mean diameter R LC of liquid crystal droplets is 2 ⁇ R LC ⁇ P.
  • R Lc is usually about 2 ⁇ m.
  • the range of the pitch P is about 4 ⁇ m or more.
  • the pitch P referred to in this description does not necessarily mean that the concave-convex portions have a periodic structure, but it means a value obtained by dividing "a unit length" by "the number of crest in the cross-sectional profile in the unit length" ("the number of crest in the cross-sectional profile” is defined in JIS B 0601-1982).
  • the depth d of the concave-convex portions is not usually uniform, but has a distribution.
  • the distribution is expressed by a mean surface roughness Ra of concave-convex deviated from the center line of the surface which is defined in JIS B 0601-1982.
  • the values Ra and G should have the optimum relation described in the equation (1): 0.03 ⁇ G ⁇ Ra ⁇ 0.3 ⁇ G
  • the mean surface roughness Ra of concave-convex deviated from the center line of the surface is in a range of 0.3 ⁇ m-3 ⁇ m.
  • the value Ra in consideration of the both concave-convex structures should satisfy the above-mentioned range. Namely, as a result, the electrode gap has the corresponding distribution according to the surface roughness.
  • the linearity in the applied voltage-transmittance characteristics can be improved and an excellent gray scale display is obtainable without a special ⁇ correction.
  • Figure 2 is a diagram showing an embodiment of a projection type liquid crystal display apparatus having the reflection type liquid crystal display element shown in Figure 1.
  • the reflection layer and the electrode is formed on the flat surface of the substrate.
  • reference numeral 11 designates a projection light source
  • numeral 12 designates a reflection type liquid crystal display element
  • numeral 13 a lens
  • numeral 14 an aperture as a device for reducing diffusion light, which projects a picture image on a projection screen (not shown).
  • light emitted from the projection light source 11 which is disposed at the left side of the liquid crystal display element in the drawing and is constituted by a lamp, a reflection mirror, a lens and so on is incident into the liquid crystal display element 12 via the lens 13.
  • the incident light is reflected at the rear side (right side) of the liquid crystal display element 12 and emits toward the left side.
  • the emitted light passes through the lens 13 and diffusion light is reduced by the aperture 14, and only light passing through the aperture 14 is projected on the projection screen.
  • the projection light source may be a conventional one, and it may be in combination of a lamp such as a metal halide lamp, a halogen lamp, a xenon lamp or the like, a lens, a mirror for light focusing such as a spherical mirror, an elliptic mirror and an aperture to obtain parallel light beams if necessary.
  • a lamp such as a metal halide lamp, a halogen lamp, a xenon lamp or the like
  • a lens a mirror for light focusing such as a spherical mirror, an elliptic mirror and an aperture to obtain parallel light beams if necessary.
  • the parallel light beams may be obtained by passing laser beams through a beam expander.
  • a dichroic prism is arranged between the lens 13 and the liquid crystal display element 12 or between the lens 13 and the aperture 14, and three liquid crystal display elements are arranged at three sides of the dichroic prism.
  • the lens 13 and the aperture 14 constitute a projection optical system.
  • the optical system is to project the straight-forward light emitted from the liquid crystal display element on a projection screen.
  • the projection lens only the lens 13 is sufficient, or an additional lens may be disposed between the lens 13 and the aperture 14 or at the light-outgoing side of the aperture 14.
  • the device for reducing diffusion light it is preferred to use such device that among incident light emitted from the liquid crystal display element, only straight-forward light is passed and diffusion light is removed.
  • an aperture having a small opening is usually used.
  • a small reflection mirror may be arranged instead of the aperture so that only straight-forward light is taken.
  • the liquid crystal display element assumes a transparent state, a scattering state and an intermediate state for each picture element in response to applied voltages.
  • incident light is regularly reflected at the reflection layer on the flat surface of the substrate at the backside of the display element and is emitted from the incident side. Since the emitting light has the same optical axis as that of regular reflection light, it passes through the aperture 14. Accordingly, there appears a bright light spot on the projection screen.
  • incident light is scattered and the scattered light is emitted from the light incident side. The major portion of the scattered light has the optical axis different from that of the regular reflection light, whereby it does not pass the aperture 14. Accordingly, there appears a dark point on the projection screen.
  • a part of incident light passes through the aperture 14, whereby a display of a half tone appears on the projection screen.
  • the liquid crystal display element shown in Figure 1 When the liquid crystal display element shown in Figure 1 is used for the display apparatus shown in Figure 2, an image-sticking phenomenon due to hysteresis can be controlled and a display having a high contrast ratio is possible.
  • reflection of incident light at the outer surface (the left side surface of the substrate placed at the left side in Figure 1) of the substrate of the liquid crystal display element reduces the contrast ratio.
  • the outer surface of the substrate should be provided with an antireflection coating of an optical interference multilayer to thereby control glaring.
  • the liquid crystal display element of the present invention has an effect to control image-sticking due to hysteresis even when it is used for a transparent type.
  • a projection light source is provided on the left side and a projection optical system is provided on the right side in Figure 2 so that light is incident to the liquid crystal display element from the left side and the light is emitted from the right side.
  • the liquid crystal and solidified matrix composite in which liquid crystal is dispersed and held in a solidified matrix is held between two substrates with electrodes at least one of which is the substrate having a concave-convex surface.
  • the liquid crystal and solidified matrix composite comprises a solidified matrix having a large number of fine holes and a nematic liquid crystal filled in the holes.
  • the liquid crystal and solidified matrix composite assumes a transparent state and a scattering state depending on conditions that a voltage is applied across the electrodes between which the liquid crystal and solidified matrix composite is held. Namely, the refractive index of the liquid crystal is changed due to an applied voltage, hence, the relation between the refractive index of the solidified matrix and the refractive index of the liquid crystal is changed. Namely, when the refractive indices are in agreement with each other, a transparent state is provided, and when not, scattering state is provided.
  • the liquid crystal and solidified matrix composite comprising the solidified matrix having a large number of fine holes and the liquid crystal filled in the holes has such a structure that liquid crystal droplets are sealed in vacuoles such as microcapsules, wherein the individual microcapsules may not be completely independent or the individual vacuoles may be communicated with each other through fine gaps like a porous material.
  • the liquid crystal and solidified matrix composite for the liquid crystal display element of the present invention can be prepared by mixing a nematic liquid crystal and a curable compound for forming the solidified matrix into a solution or a latex, by curing the solution or the latex by the application of light or heat, or by removing or by subjecting it to reactive curing to thereby separate the curable compound, whereby the nematic liquid crystal is dispersed in the solidified matrix.
  • photo-curable or heat-curable type compound Use of a photo-curable or heat-curable type compound is preferred since it can be cured in an enclosed system.
  • use of a photo-curable type compound is preferred since it can be cured in a short period of time with little influence of heat.
  • a cell may be formed by using a sealing material, uncured mixture of a nematic liquid crystal and a curable compound is injected through an injection port in the same manner as the conventional method, and after sealing the injection port, they can be cured by light irradiation or heating.
  • liquid crystal display element according to the present invention may also be prepared without using a sealing material, for example, by supplying an uncured mixture of the nematic liquid crystal and the curable compound on a substrate with an electrode, overlaying another substrate with an electrode on that substrate, and then curing the material by means of light irradiation or the like.
  • the periphery of the display element may be sealed by coating the sealing material.
  • coating since it is only required to supply the uncured mixture of the nematic liquid crystal and the curable compound by means of coating such as roll. coating, spin coating, printing or the method of using a dispenser or the like, the injection step is simple and productivity is extremely high.
  • the uncured mixture of the nematic liquid crystal and the curable compound may be incorporated with spacers for controlling the inter-substrate gap such as ceramic particles, plastic particles or glass fibers, pigments, dyes, viscosity controllers or any other additives which do not adversely influence to the performance of the liquid crystal display element of the present invention.
  • liquid crystal and solidified matrix composite having a specific resistance of 5 ⁇ 10 9 ⁇ cm or higher is preferable.
  • Use of such one having a specific resistance of 10 10 ⁇ cm or higher is more preferable in order to minimize voltage drop caused by a leakage current. This reduces electric power consumption.
  • a liquid crystal display element in which an active element is used for each picture element it is unnecessary to provide a relatively large capacitance to each picture element electrode.
  • the haze value in a scattering state is preferably not less than 80%.
  • the liquid crystal display element of the present invention is so adapted that in either state of voltage application or no voltage application, the refractive index of the solidified matrix (after curing) agrees with the refractive index of the liquid crystal used, and in the opposite state, the refractive index of the solidified matrix does not agrees with the refractive index of the liquid crystal used.
  • the refractive index of the solidified matrix agrees with the ordinary refractive index (n 0 ) of the liquid crystal used, in a state of applying a voltage.
  • the display element exhibits a transparent state when a voltage is applied to, whereby the transmittance in a transparent state becomes high and a uniform transparent state is obtainable. Accordingly, a display having a high contrast ratio can be provided.
  • the refractive index anisotropy should be ⁇ n>0.18, more preferably ⁇ n>0.22.
  • the ordinary refractive index n 0 of the liquid crystal used substantially agrees with the refractive index n p of the solidified matrix, whereby a high transparency is obtainable when a voltage is applied.
  • a relation of n 0 -0.03 ⁇ n p ⁇ n 0 +0.05 should be satisfied.
  • the volume fraction ⁇ of the liquid crystal which is operable in the liquid crystal and solidified matrix composite In order to improve the scattering ability when no voltage is applied, it is effective to increase the volume fraction ⁇ of the liquid crystal which is operable in the liquid crystal and solidified matrix composite.
  • the range of ⁇ >20% is preferred.
  • the value ⁇ is excessively large, the stability in structure of the liquid crystal and solidified matrix composite becomes inferior. Accordingly, it is preferable that ⁇ 70%.
  • a scattering state i.e., an opaque state
  • a difference in refractive index between the liquid crystal which is not arranged in parallel in a specified direction and the solidified matrix when no voltage is applied.
  • the portion other than picture elements scatteres light and looks dark because light does not reach a projection screen without providing a light shielding layer at the portion other than the picture elements. From this, it is unnecessary to provide a light shielding layer for the portion other than the picture element electrodes in order to prevent light from leaking from any other portion of the liquid crystal display element than the picture element electrodes. Accordingly, there is an advantage that the step of forming the light shielding layer is unnecessary.
  • a voltage is applied to a desired picture element.
  • the liquid crystal is oriented so that the ordinary refractive index (n 0 ) of the liquid crystal and the refractive index (n p ) of the solidified matrix agree with each other, and accordingly, the liquid crystal display element presents a transparent state. Then, light is transmitted through desired picture elements to thereby provide a bright display on a projection screen.
  • a photo-curable vinyl compound is preferably used.
  • a photo-curable acryl compound and particularly, those containing acryl oligomer which is curable upon polymerization under the irradiation of light are particularly preferred.
  • the liquid crystal used in the present invention is preferably a nematic liquid crystal having a positive dielectric anisotropy.
  • liquid crystal wnerein the refractive index of the solidified matrix agrees with the refractive index of the liquid crystal when a voltage is applied or no voltage is applied.
  • Such liquid crystal may be used solely or may be used as a composition, and use of a composition can be advantageous because various demands such as working temperature range, working voltage and so on are satisfied. It is, in particular, preferable to use such liquid that the refractive index of the solidified matrix agrees with the ordinary refractive index (n 0 ) of the liquid.
  • liquid crystal and solidified matrix composite When a photo-curable compound is used for the liquid crystal and solidified matrix composite, it is preferable for the liquid crystal to uniformly dissolve the photo-curable compound. A cured material after exposure to light can not be dissolved or is hardly dissolved. When liquid crystal is used as a composition, it is preferable to use each liquid crystal having a closer value in solubility.
  • liquid crystal is used as solvent in the liquid crystal and solidified matrix composite, and a photo-curable compound is cured by exposing it to light. It is unnecessary to evaporate water or solvent which becomes needless when the compound is cured. Accordingly, a conventional method of injecting a curable compound in a cell can be utilized as it is because the photo-curable compound is cured in a closed system whereby reliability is high. Further, since the photo-curable compound is capable of bonding two substrates, reliability is higher.
  • one substrate has a concave-convex surface and the liquid crystal and solidified matrix composite is interposed between the two substrates, a danger of short-circuitting at a small gap portion can be minimized. Further, it is unnecessary to strictly control the orientation of liquid crystal and the inter-substrate gap as in the conventional TN type liquid crystal display element. Accordingly, a liquid crystal display element capable of controlling a transparent state and a scattering state can be efficiently produced.
  • silicone is suitable as a semiconductor material.
  • Polycrystalline silicone is particularly preferred since it has less photosensitivity as in amorphous silicone and, accordingly, does not cause erroneous operation even without shielding light from a light source by means of a light shielding film.
  • a strong light source for projection can be utilized and a bright display is obtainable.
  • liquid crystal and solidified matrix composite wherein the refractive index of the solidified matrix substantially agrees with the ordinary refractive index (n 0 ) of the liquid crystal is used. Accordingly, light is scattered at the portion not applied with an electric field, and it appears dark on the projection screen. Accordingly, there is no requirement for forming the light shielding film in the portion where no voltage is applied, between the picture elements.
  • the step of forming the light shielding film can be eliminated or severe requirements to the light shielding film can be reduced, whereby the number of manufacturing steps can be reduced and the productivity is improved.
  • an infrared ray cut filter, an ultraviolet-ray cut filter, a color filter or the like may be used in a lamination form; a cooling system may be added; a reinforcing glass sheet may be laminated, or characters, figures or the like may be printed. Further, a plurality of liquid crystal display elements may be used. In addition, a dichroic mirror, a dichroic prism or a mirror may be used so that light from a light source is separated or light emitted from the liquid crystal display element is collected.
  • At least one substrate with an electrode between the two substrates with electrodes is provided with a fine concave-convex electrode surface at the side for the liquid crystal and solidified matrix composite. Accordingly, there is a distribution of thickness of the electrode gap and the electric field across the liquid crystal and solidified matrix composite is distributed. As a result, the threshold voltage value of the composite is dispersed, whereby an image-sticking phenomenon due to hysteresis can be controlled.
  • the control of the image-sticking is effected only by controlling a concave-convex portion of substrate.
  • the allowable range of control is wide, and the productivity is excellent. Accordingly, a beautiful display is obtainable even in a half tone display.
  • liquid crystal display element When the liquid crystal display element is used for a reflection type liquid crystal display, a concave-convex portion is formed in the substrate at the light-incident side, whereby glare, i.e. regular reflection can be controlled and the contrast ratio of display is improved.
  • a nematic liquid crystal having a positive dielectric anisotropy, acrylate monomer, urethane acrylate oligomer and a photo-cure initiator were uniformly dissolved to prepare solution.
  • a cell was prepared by using a TFT substrate with a TFT for each picture element transparent electrode on the flat surface, a counter electrode substrate having a counter transparent electrode and spacers each having a diameter of 10 ⁇ m.
  • the previously prepared solution was injected into the cell and the solution was cured by irradiating ultraviolet-rays to form a liquid crystal and solidified matrix composite.
  • the average diameter of liquid crystal droplets R LC was about 2 ⁇ m.
  • the size of picture element was about 200 ⁇ m ⁇ 200 ⁇ m.
  • a concave-convex treatment was conducted to the portion of the counter electrode substrate in contact with the liquid crystal and polymer composite.
  • the pitch and the depth of the concave-convex portion were respectively 20 ⁇ m and 4 ⁇ m, and the mean surface roughness Ra of the concave-convex portion was about 1 ⁇ m.
  • ITO was vapor-deposited on the concave-convex surface to form a counter electrode.
  • the average inter-electrode gap was about 12 ⁇ m.
  • a projection type liquid crystal display apparatus was prepared by using the transmissive type liquid crystal display element, a projection light source and a projection optical system. As a result of tests, a dynamic display having a contrast ratio of 120 was obtained on a projection screen. In the measurement of the applied voltage-transmittance characteristic of the display element, the transmittance at 7V was 70%. The hysteresis was very small to the extent that the maximum difference in transmittance between a voltage increase time and a voltage decrease time was 2.8% wherein voltage was increased from 0V to 10V and then was reduced to 0V.
  • a cell was prepared in the same manner as Example 1 except that the counter substrate was a flat substrate on which ITO was vapor-deposited and the average inter-electrode gap was 12 ⁇ m which was the same value as that of Example 1.
  • a liquid crystal and polymer composite was prepared in the same manner as Example 1 to form a display cell. When the display element was driven by applied a voltage of about 7V, an image-sticking phenomenon was found in display.
  • a projection type display apparatus was prepared in the same manner as Example 1. It was found that the contrast ratio on the projection screen was about 130. As a result of measurement of the applied voltage-transmittance characteristic of the display element, the transmittance at 7V was 71%, and the maximum difference of the transmittance due to hysteresis was 5.0%.
  • Liquid crystal display elements were prepared in the same manner as Example 1 except that the mean electrode gap G ( ⁇ m) and the mean surface roughness Ra ( ⁇ m) of concave-convex portions of the substrate having a concave-convex surface of each of the display elements were determined as shown in Table 1.
  • the contrast ratio CR on a projection screen, the transmittance T 7V (%) and the maximum difference of the transmittance ⁇ T (%) due to hysteresis of projection type display apparatuses in which the above-mentioned display elements were installed, are also shown in Table 1.
  • a liquid crystal display element was prepared in the same manner as Example 1, and a projection type liquid crystal display apparatus was prepared by combining the liquid crystal display element with a projection light source and a projection optical system wherein the electrodes of the TFT substrates were made of aluminum which were used as reflection type elements, and an antireflection coating of an optical interference multilayer was provided on the outer surface of the electrode of the counter electrode substrate.
  • the average inter-electrode gap was about 10 ⁇ m
  • the pitch P of concave-convex was about 9 ⁇ m
  • the depth of concave-convex was about 1.3 ⁇ m
  • Ra was about 0.4 ⁇ m.
  • the degree of collimation for incident light into the liquid crystal display element was about twice larger than that of Example 1 to 3.
  • the projection type liquid crystal display apparatus was driven by a video signal of a driving voltage of about 6V. As a result, a dynamic display free from image-sticking was obtained.
  • the contrast ratio on the projection screen was 110 and the screen brightness was about twice more than that of Example 1.
  • Liquid crystal display element was prepared in the same manner as Example 1 except that the pitch was 3 ⁇ m and Ra was 0.5 ⁇ m. As a result of tests, the contrast ratio was 90, T 7V was 65% and ⁇ T was 4.8%. The transmittance and the contrast ratio were slightly reduced and (the effect of reducing hysteresis) was not substantially found.
  • the threshold voltage is dispersed to thereby apparently reduce the hysteresis on the applied voltage-transmittance characteristic of the liquid crystal and solidified matrix composite. Accordingly, the image-sticking of an image can be reduced and a beautiful half tone display can be provided. Further, the linearity of the applied voltage-transmittance characteristic is improved and an excellent gray scale display can be obtained without a special ⁇ correction.
  • regular reflection can be eliminated because the interface between the liquid crystal and solidified matrix composite and at least one substrate with an electrode is inclined to the mean flat face of the substrate surface.
  • the liquid crystal display element is used for a projection type display apparatus, reduction of the contrast ratio due to reflection light can be prevented.
  • the reflection type liquid crystal display element of the present invention is used for projection type display apparatus wherein the counter electrode on the flat substrate surface is used as a reflection layer, reduction of the contrast ratio due to regular reflection at the interface between the liquid crystal and solidified matrix and transparent electrode can be remarkably improved.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Mathematical Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Liquid Crystal (AREA)

Claims (10)

  1. Elément d'affichage à cristaux liquides comprenant des substrats dont au moins l'un est transparent, et des électrodes dont au moins l'une est transparente, et un composite de cristaux liquides et de matrice solidifiée, dans lequel les cristaux liquides sont dispersés et retenus dans une matrice solidifiée, et qui est intercalé entre une paire d'électrodes, situées face à face, caractérisé en ce qu'il existe des différences quant aux distances entre les électrodes en diverses parties, dans lesquelles l'électrode transparente du premier substrat transparent a une surface concavo-convexe à pas fin, et l'électrode du deuxième substrat a une surface plate sur le côté correspondant au composite de cristaux liquides et de matrice solidifiée.
  2. Elément d'affichage à cristaux liquides selon la revendication 1, dans lequel la relation 0,03 · G < Ra < 0,3 · G est satisfaite, G étant l'espace moyen entre électrodes, et Ra étant la rugosité moyenne de surface d'aspect concavo-convexe par rapport à la ligne médiane de la surface.
  3. Elément d'affichage à cristaux liquides selon la revendication 1 ou 2, dans lequel le pas P de la surface concavo-convexe est deux fois plus grand, ou davantage, que le diamètre moyen RLC des gouttelettes de cristal liquide.
  4. Elément d'affichage à cristaux liquides selon la revendication 3, dans lequel la taille des éléments d'image est comprise entre environ 30 µm et 200 µm, et le pas P de la surface concavo-convexe est de 100 µm ou moins.
  5. Elément d'affichage à cristaux liquides selon l'une des revendications 1 à 4, dans lequel une couche à faible réflexion d'une multicouche d'interférence optique est disposée au niveau du côté de la surface extérieure du substrat ayant une surface concavo-convexe.
  6. Elément d'affichage à cristaux liquides selon l'une des revendications 1 à 5, dans lequel l'indice de réfraction de la matrice solidifiée concorde avec l'indice ordinaire de réfraction (n0) du cristal liquide utilisé, lorsqu'une tension est appliquée au composite de cristaux liquides et de matrice solidifiée.
  7. Appareil d'affichage à cristaux liquides du type à projection, comprenant un élément d'affichage à cristaux liquides comportant un premier substrat transparent ayant une électrode transparente, un deuxième substrat ayant une électrode et une couche de réflexion, et un composite de cristaux liquides et de matrice solidifiée, dans lequel les cristaux liquides sont dispersés et retenus dans une matrice solidifiée, et qui est intercalé entre ladite paire de substrats, une source de lumière de projection, pour émettre de la lumière vers l'élément d'affichage à cristaux liquides, et un système optique de projection comprenant au moins une lentille et une ouverture, caractérisé en ce que l'électrode transparente du premier substrat transparent a une surface concavo-convexe à pas fin, et en ce que l'électrode du deuxième substrat a une surface plate sur le côté correspondant à l'interface du composite de cristaux liquides et de matrice solidifiée.
  8. Appareil d'affichage à cristaux liquides du type à projection, comprenant un élément d'affichage à cristaux liquides défini dans l'une quelconque des revendications 1 à 6, et un circuit d'attaque pour attaquer l'élément d'affichage, dans lequel le circuit d'attaque permet d'appliquer plusieurs tensions, inférieures à une tension de seuil, pour une présentation à demi-teintes.
  9. Appareil d'affichage à cristaux liquides du type à projection, comprenant un élément d'affichage à cristaux liquides défini dans l'une quelconque des revendications 1 à 6, un circuit d'attaque pour attaquer l'élément d'affichage, une source de lumière de projection pour émettre de la lumière vers l'élément d'affichage à cristaux liquides, et un système optique de projection pour projeter la lumière à partir de l'élément d'affichage à cristaux liquides sur un écran de projection.
  10. Appareil d'affichage à cristaux liquides du type à projection selon l'une quelconque des revendications 7 à 9, dans lequel un dispositif servant à réduire la lumière de diffusion est placé dans un chemin de la lumière venant de l'élément d'affichage à cristaux liquides, qui a une valeur de flou non inférieure à 80 % à l'état de dispersion.
EP92114825A 1991-08-30 1992-08-28 Elément d'affichage à cristal liquide et appareil d'affichage à cristal liquide utilisant celui-ci Expired - Lifetime EP0529672B1 (fr)

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JP24513691 1991-08-30

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JP2768313B2 (ja) * 1995-06-13 1998-06-25 日本電気株式会社 反射型液晶表示装置
JP2990046B2 (ja) * 1995-08-16 1999-12-13 日本電気株式会社 反射型液晶表示装置及びその製造方法
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JP5691467B2 (ja) * 2010-12-10 2015-04-01 旭硝子株式会社 投射型表示装置
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JP2022129506A (ja) * 2021-02-25 2022-09-06 日東電工株式会社 加飾フィルム

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US5283675A (en) 1994-02-01
EP0529672A3 (en) 1993-09-22
EP0529672A2 (fr) 1993-03-03
DE69223002T2 (de) 1998-03-05
DE69223002D1 (de) 1997-12-11

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